Sixty years later, the incident was described by The New York Times as "one of the worst air pollution disasters in the nation's history".[2] Even 10 years after the incident, mortality rates in Donora were significantly higher than those in other communities nearby.[3]

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The fog started building up in Donora on October 27, 1948. By the following day it was causing coughing and other signs of respiratory distress for many residents of the community in the Monongahela River valley. Many of the illnesses and deaths were initially attributed to asthma. The smog continued until it rained on October 31, by which time 20 residents of Donora had died and approximately one third to one half of the town's population of 14,000 residents had been sickened. Another 50 residents died of respiratory causes within a month after the incident; notable among the fatalities was Lukasz Musial, the father of future baseball Hall of Famer Stan Musial, the 1948 National League MVP.

Hydrogen fluoride and sulfur dioxide emissions from U.S. Steel's Donora Zinc Works and its American Steel & Wire plant were frequent occurrences in Donora. What made the 1948 event more severe was a temperature inversion, a situation in which warmer air aloft traps pollution in a layer of colder air near the surface. The pollutants in the air mixed with fog to form a thick, yellowish, acrid smog that hung over Donora for five days. The sulfuric acid, nitrogen dioxide, fluorine, and other poisonous gases that usually dispersed into the atmosphere were caught in the inversion and accumulated until rain ended the weather pattern.[2]

Two of the heroes to emerge during the four-day smog were Chief John Volk of the Donora Fire Department and his assistant Russell Davis. Volk and Davis responded to calls from Friday night until Sunday night, depleting their supply of 800 cubic feet (23 m3) of oxygen, borrowing more from all nearby municipalities, including McKeesport, Monessen, and Charleroi. "I didn’t take any myself. What I did every time I came back to the station was have a little shot of whiskey."

The eight doctors in the town, who belonged to the Donora Medical Association, made house calls much like the firefighters during the period of intense smog, often visiting the houses of patients who were treated by the other doctors in town. This was a result of patients calling every doctor in town in the hope of getting treatment faster. It was not until mid-day Saturday that Mrs. Cora Vernon, executive director of the American Red Cross, had it set up so that all calls going to the doctors’ offices would be switched to the emergency center being established in the town hall. The smog was so intense that driving was nearly abandoned; those who chose to continue driving were risky. “I drove on the left side of the street with my head out the window. Steering by scraping the curb.” recalls Davis.

It was not until Sunday morning, the 31st of October, that a meeting occurred between the operators of the plants, and the town officials. Burgess Chambon requested the plants temporarily cease operations. The superintendent of the plants, L.J. Westhaver, said the plants had already begun shutting down operation at around 6 a.m. that morning. With the rain alleviating the smog, the plants resumed normal operation the following morning.

Researchers analyzing the event have focused likely blame on pollutants from the zinc plant, whose emissions had killed almost all vegetation within a half-mile radius of the plant.[2] Dr. Devra L. Davis, director of the Center for Environmental Oncology at the University of Pittsburgh Cancer Institute, has pointed to autopsy results showing fluorine levels in victims in the lethal range, as much as 20 times higher than normal. Fluorine gas generated in the zinc smelting process became trapped by the stagnant air and was the primary cause of the deaths.[3] Further research was conducted by Mary Amdur about the effects of the smog; she was pressured to withdraw publication of these results but refused to be bowed.[4]

Preliminary results of a study performed by Dr. Clarence A. Mills of the University of Cincinnati and released in December 1948 showed that thousands more Donora residents could have been killed if the smog had lasted any longer than it had.[5]

Lawsuits were filed against U.S. Steel, which never acknowledged responsibility for the incident, calling it "an act of God".[2] While the steel company did not accept blame, it reached a settlement in 1951 in which it paid about $235,000, which was stretched over the 80 victims who had participated in the lawsuit, leaving them little after legal expenses were factored in. Representatives of American Steel and Wire settled the more than $4.6 million claimed in 130 damage suits at about 5% of what had been sought, noting that the company was prepared to show at trial that the smog had been caused by a "freak weather condition" that trapped over Donora "all of the smog coming from the homes, railroads, the steamboats, and the exhaust from automobiles, as well as the effluents from its plants."[3][6] U.S. Steel closed both plants by 1966.[2]

By 1949, a year after the disaster, the total value of the predominantly residential property in Donora had declined by nearly 10%.[6]

The Donora Smog was one of the incidents where Americans recognized that exposure to large amounts of pollution in a short period of time can result in injuries and fatalities. The event is often credited for helping to trigger the clean-air movement in the United States, whose crowning achievement was the Clean Air Act of 1970, which required the United States Environmental Protection Agency to develop and enforce regulations to protect the general public from exposure to hazardous airborne contaminants.[2]

The incident was little spoken of in Donora until a historical marker was placed in the town in 1998, to commemorate the 50th anniversary of the incident. The 60th anniversary, in 2008, was commemorated with memorials for the families of the victims and other educational programs. The Donora Smog Museum was opened on October 20, 2008, located in an old storefront at 595 McKean Avenue near Sixth Street, with the slogan "Clean Air Started Here". Fewer than 6,000 people still live in Donora.[2]

The 2009 novel Don't Kill the Messenger by Joel Pierson features a fictional town, Wyandotte, Pennsylvania, which became a ghost town after a smog incident, based on the Donora Smog.[10]

An hour-long documentary, Rumor of Blue Sky, produced by Andrew Maietta and Janet Whitney, aired on WQED TV in April 2009. The film features archival images and interviews with survivors of the environmental tragedy.